8. (y⁴)⁻⁵ / y⁻¹⁹ при y=10;

1. y⁻²⁰ / y⁻¹⁹ = y⁻²⁰⁻⁽⁻¹⁹⁾ = y⁻¹.

2. Substitute y=10: 10⁻¹ = 1/10.